1. Field of the Invention
The present invention relates to a method of and apparatus for recording data on an optical recording medium, and more particularly, to a method of and apparatus for recording channel-modulated digital data on an optical disc by forming a mark or a space thereon.
2. Description of the Related Art
In general, data is recorded on an optical disc, which is one type of optical recording media, by forming a mark or a space on a target track of the optical disc. In the case of read-only discs such as CD-ROMs and DVD-ROMs, the mark or the space is formed as a pit. In the case of a writable disc such as CD-R/RW or DVD-R/RW/RAM, a recording layer is coated with a phase change material whose properties change into crystalline or amorphous crystalline according to temperature. By using such characteristics of the phase change material, the mark or the space is formed on a writable disc.
Data recording methods using signal detection are divided into a mark edge recording method and a mark position recording method. The mark position recording method uses the amplitude of a detected radio-frequency (RF) signal change from a positive/negative value to a negative/positive value, starting from the position of the mark. In contrast, the mark edge recording method uses a feature in which the amplitude of a detected RF signal changes from a positive/negative value to a negative/positive value in order to start from the both edges of a mark. Thus, the edge of the mark must be precisely recorded on the target track of an optical medium so as to improve the quality of a reproduction signal.
However, in an optical disc having the phase change film, the shape of the trailing edge of a mark, which is recorded by such a conventional recording method, depends on the length of the mark or an interval between adjacent marks (i.e., the length of the space). For instance, the size of the trailing edge of a mark may be larger than that of its leading edge, thereby deteriorating the recording/reproducing characteristics of the optical disc. The recording/reproducing characteristics become much worse because heat is accumulated in the edge of a mark when a recording mark is comparatively long.
FIGS. 1A through 1C illustrate a conventional recording waveform for recording non-return-to-zero-inverted (NRZI) data on a DVD+RW. Here, T denotes a period of a reference clock. In the mark edge recording method, high and low levels of the NRZI data are recorded as the mark and the space, respectively. A recording waveform for recording a mark and a recording waveform for recording a space (for erasing the mark) are called a record pattern and an erase pattern, respectively. A conventional recording waveform includes the record pattern, the record pattern being a multi pulse having a plurality of unit pulses that are maintained at the same power levels for the same time, and includes the erase pattern that is maintained at a predetermined DC level for a predetermined duration.
Specifically, the erase pattern included in the conventional recording waveform is maintained at a predetermined DC level for a predetermined time, resulting in the continuous heating of an area of an optical disc where the erase pattern is recorded, at a temperature between 0° C. and 200° C. If the erase pattern is repeatedly recorded a predetermined number of times, the quality of the optical disc deteriorates. Thus, the mark recorded on the optical disc distorts, thereby remarkably lowering the recording/reproducing characteristics of the optical disc.
In particular, the recording/reproducing characteristics deteriorate to a great extent when a period T of a reference clock becomes shorter and the thermal interference between pulses of a recording waveform increases as the recording density and linear velocity of an optical disc are increased so as to record much more data. Further, when the conventional record pattern has a multi-pulse, the amount of power supplied to record the mark may decrease to distort the mark when data is recoded on an optical disc at a high speed so as to increase the transmission speed of data (i.e., when the period T of the reference clock decreases).